1. Field of the Invention
The present invention relates generally to the field of charging electronic devices and more particularly to system and method for accomplishing this when a particular power source cannot supply enough power to charge a particular ensemble of devices at the same time.
2. Description of the Prior Art
In environments such as schools and the like, numerous small electronic devices such as tablet and laptop computers, smartphones and the like may need charging. Prior art methods include lockers containing power receptacles where these devices can be placed for overnight charging.
However, there is a major problem with charging such devices: they draw considerable charging current from the power line, and they continue to draw this current even after the device is fully charged. For example, a tablet computer may draw around 0.85 Amperes from the AC line, while a laptop may draw as much as 2.2 Amperes. A typical 15 Ampere outlet can thus only charge six laptops of this type at one time. This creates a problem because a typical charging situation may require that 20-30 devices be charged overnight for use the next day.
Prior art solutions to this problem use multiple separate 15 Ampere outlets with multiple cords, or require a much higher amperage supply such as a 20 Ampere or higher outlet. According to the National Electrical Code, a 20 Ampere outlet requires at least #12 AWG wiring. This is expensive and must be specially installed. The use of multiple 15 Ampere outlets usually requires several extension cords (since they are seldom located together), and the total power draw, safety considerations and related cost is considerable.
For example, to charge 24 appliances each requiring 2.2 Amperes is a total current draw of 52.8 Amperes or over 6000 Watts RMS (at 120 Volts RMS). While many devices do not require this much charging current, a classroom having 30 students each with a 0.85 Ampere device can require as much as 25.5 Amperes total AC charging current or over 3000 Watts.
Since devices normally do not require charging for more than a few hours at most, it would be very advantageous to have a charging system that could take advantage of this, and switch different devices in and out for charging during a total charging period (say overnight) thus allowing the use of a single 15 Ampere outlet to power a charging cabinet.